Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $215.51   8.268%   $233.3284   $233.33   $233.35   $233.30  
  Purchase #2 $206.94   6.152%   $219.6709   $219.67   $219.65   $219.70  
  Purchase #3 $233.83   3.230%   $241.3827   $241.38   $241.40   $241.40  
  Purchase #4 $189.61   13.285%   $214.7997   $214.80   $214.80   $214.80  
  Purchase #5 $240.92   11.445%   $268.4933   $268.49   $268.50   $268.50  
  Purchase #6 $34.61   13.478%   $39.2747   $39.27   $39.25   $39.30  
  Purchase #7 $93.77   3.789%   $97.3229   $97.32   $97.30   $97.30  
  7 purchase totals = $1,215.19       $1,314.2726   $1,314.26   $1,314.25   $1,314.30